Molecularly oriented copolymers of acrylonitrile, a vinyl aryl compound, and acrylicesters or vinyl ethers



' radicals.

Patented Mar. 11, 1947 UNITED sures PATENT ornce MOLECULARLY ORIENTED COPOLYMERS OF ACRYLONITRILE, A VINYL ARYL COM- POUND, AND ACRYLIC ESTERS OR VINYL ETHERS Gaetano F; DAlello, Northampton, Mass., assignor to Pro-phy-lac-tic Brush Company, Northampton, Mass., a corporation of Delaware No Drawing. Application February 25,1944,

Serial No. 523,904

4 Claims. (01. 260-32) This invention relates to novel synthetic compositions comprising copolymers of acrylonitrile,

' and a vinyl aryl compound and another polymerizable monomer selected from the class of acrylic esters and vinyl ethers. The invention also relates to formed structures wherein the molecules have been oriented so that they are parallel with the major surface and which exhibit characteristic X-ray diffraction patterns.

Acrylonitrile has the formula CH2==CHCN. I may use a vinyl aryl compound or an organic compound of the structure CH2=CRZ wherein R i hydrogen and a methyl radical and Z is an aryl radical, examples of which are phenyl; the chlorphenyls; for example, the

' mono-, di-, and trichlorphenyls; the l'iltlODhi-lllr yls; tolyl; the carbalkoxyphenyls; for example,

the methyl, ethyl, and propyl derivatives, etc.

As specific examples of such aryl compounds may be mentioned styrene, isopropenyl benzene,

. solvent actions of many chemical bodies.

isopropenyl toluene, monochlorstyrene, dichlorstyrene, trichlorstyrene, vinyl methyl benzoate, vinyl ethyl benzoate, nitrostyrene, nitrovinyl toluene, etc.

The acrylic esters used in the practice of this invention have the structural formula CHFC-G 0 OR where R is a radical selected from the class of hydrogen and methyl radicals. Examples of radicals which may be represented by R are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, secondary amyl, isoamyl, mixed amyl, hexyl, cyclopentyl, cyclohexyl, methyl cyclopentyl, methylcyclohexyl, benzyl, phenethyl, chloroethyl,

softening point and is extremely resistant to the Likewise, polyacrylonitrile is far too hard and brittle and has too high a softening-point to be used in the preparation of extruded or precipitated bodies wherein the molecules have been oriented so that they are parallel with the major surface.

- It has been known for some time that when acrylonitrile iscopolymerized with certain suitable monomers, the properties of the copolymer are considerably altered even by small quantities of other monomers, and that, from these copolymers, itis possible to produce workable masses.

However, it is now recognized that many of these copolymers possess a new element and property in that they are capable of being converted, as

for example, by-cold drawing, into products and structures wherein the molecules have been oriented so that they are parallel with the major surface and whereby the formed structures exhibit characteristic X-ray diffraction patterns.

In my copending applications, Serial No. 445,- 808, filed June 4, 1942; Serial No. 449,678, filed July 3, 1943; and Serial Nos. 523,901, filed February 25, 1944, 523,902, filed February 25, 1944,

and 523,903, filed February 25, 1944, certain comethods, could not be cold drawn to give orientacetoxyethyl, methoxyethyl,ethoxyethyl, butoxyethyl, phenoxyethyl, chlorphenoxyethyl, acetoxypropyl, methoxypropyl, ethoxypropyl, phenoxypropyl, carbalkoxyethyl, secondary butyl, propyl cyclopentyl, amyl cyclopentyl, dimethyl cyclohexyl, phenyl, zenyl, tolyl, xylyl, ethyl phenyl, propyl phenyl, isopropyl phenyl, phenyl propyl,- phenyl butyl, etc. As noted, all of these acrylic ed products when copolymerized with such unsaturated compounds as butadiene, styrene, diethyl maleate, and vinyl acetate. This behavior is not surprising since even at the present state of the art, it is impossible to predict what comesters contain a single polymerizable unsaturated v double bond in the acrylic acid residue.

The monovinyl ethers used in the practice of this invention have the formula CI-lz=CHOR where R has the same meaning as the radical used in the acrylic esters mentioned heretofore. In general, in the above formulas, the term R is a radica1 selected from the class of alkyl radicals, aralkyl radicals,'aryl radicals, and alkaryl Acrylonitrile itself, when polymerized, possesses characteristic properties in that it has a very high pounds'will yield satisfactory cold-drawn fiberor film-forming compositions. This is true even of polymeric vinylidene chloride as emphasized in the United States Patent No.- 2,233,442 which states that only selected copolymers'will yield satisfactory products; e. g., Most of the materials copolymerized with the vinylidene chloride do not. in themselves exhibit characteristic X- 'ray diffraction patterns, and many of the copolymers of vinylidene chloride containing large proportions of these materials are similarly incapable of being drawn into strong pliable articles.

Generally speaking, it may be stated that thernioplastic polymers and copolymers of all types possess little or-no tendency to form the crystalline patterns exhibited by the compositions of the present invention.v

As disclosed in my aforementioned copending 3 applications, it was shown that not all copoly-' mers of acrylonitrile could be drawn into objects that possessed molecularly oriented structures along the major axis and which exhibited'characteristic X-ray diffraction patterns. Previous attempts to prepare suitable copolymers of acrylonitrile and a vinyl. aryl compound which would be suitable to produce cold drawn and oriented products have been unsuccessful. The copolymers of acrylonitrile and vinyl aryl compounds are extremely difficult to prepare. This is particularly true when attempts are made to prepare copolymers which would have sufficient acrylonitrile so that the-cold drawing properties may be obtained. Even when copolymers of the desired composition are obtained, such compositions cannot be satisfactorily cold drawn to produce the oriented products of this invention. as illustrated in the following examples:

Example 1 a b c Parts Paris Paris Acrylonitrile 45 40 35 Styrene 5 l0 l5 Bonzoyl peroxide 0. 25 0. 25 (i. 2!

Example 2 Even when the copolymer is preparedby granulation methods, as in the following example, the copolymer could not be cold drawn. and, furthermore, was insoluble in all the ordinary solvents tested, such as acetone, ethyl alcohol and acetic acid.

Parts by weight Acrylonitrile '70 Styrene 30 Benzoyl peroxide 1 Polyvinyl alcohol 2 Distilled water 400 The polyvinyl alcohol is dissolved in the water prior to the addition of the remaining ingredients. The mixture is then heated under agitation at to C. until the polymerization is completed. The granular material was then filtered oil, washed with distilled water, and dried in a vacuum oven at 60 C. for 18 hours.

I have now discovered it is possibl to produce suitable copolymers of acrylonitrile and a vinyl aryi compound if the copolymerization is carried out in the presence of another monomer selected from the class of acrylic esters and vinyl ethers as hereinbefore defined. I have also discovered that it is possible to improve the properties of certain copolymers of the invention by cold drawing if the copolymer is obtained by polymerizing a mass comprising as the primary polymerizable ingredients the three components within the following stated ratios:

Parts 70 Acrylonltrile 55 to 85 A vinyl aryl compound 5to 30 A third component 5 to 30 where the third component is selected from the class of the acrylic esters andthe vinyl ethers asprevlously defined. I 4.

These results are unexpected since the components, when polymerized. by themselves, are not capable of being c'old drawn. For example, polystyrene, polyacrylic esters or the polyvinyl others do not exhibit characteristic X-ray diffraction patterns when they are cold drawn. Furthermore, copolymers of the acrylic esters and the vinyl ethers are not satisfactory for the preparation of oriented copolymers exhibiting chars acteristic X-ray diffraction patterns.

these copolymers. If the combined value of the vinyl aryl compound and the third component, such as the acrylic ester or the vinyl ether exceeds substantially 45%, the copolymer loses a substantial part of the property whereby it can be cold drawn.

The preferred method of forming the oriented articles of this invention involves first, the copolymerization of the selected monomers. Two satisfactory methods of polymerization may be used,

the mixture of monomers may be heated along in the presence of an activating-catalyst at a temperature below the boiling point of the mass. As the polymerization proceeds, the temperature may be increased as the vapor pressure of the mass decreases. The copolymer may be freed from any monomer or low molecular weight substances by any of several methods, as, for example, by extracting the polymer with methyl alcohol or steam distilling the polymer.

Alternately, emulsion or granulation polymerization methods may be employed. The granulation method is preferred. This method involves introducing the mixture of monomers, for

example, the acrylonitrile, the styrene, and the vinyl ether, into aqueous solutions containing granulating agents.

Granulating agents are protective colloids which have relatively poor dispersing properties whereby they form nuclei for the formation of the granules of the heteropolymer. Such agents are usually called granulating agents and this process may be defined as the method of preparing these copolymers in granular form which comprise dispersing the polyinerizable mixture under agitation.

\ Examples of such protective colloids and granulating agents are soluble starch, methyl starch,

Y polyvinyl alcohol, partially hydrolyzed polyvinyl catalyst. In general, between 0.1 and 2.0% of catalyst is used depending on the nature of the catalyst and upon the desired rate of polymer-. ization. Part of the catalyst may be introduced at the initiation of the reaction and the remainder during the course of polymerization, v

The ratio of the dispersed phase, that is, the mixture of the polymerizable monomers, to the dispersing phase, the water used with the emulsifying agent or protective colloid, may be varied widely. Satisfactory results are obtained in the range of 100 parts of monomer mixture to 100 to 500 part of the dispersing phase.

Auxiliary organic solvents may likewise be used in the presence of dispersed and dispersing phases, such as dioxane, ethyl alcohol, ethyl acetate, etc. These ingredients may be added directly to the polyme'rizable mixture or may be present as diluents in the reacting ingredients.

In the ordinary method of producing the granuingredients, the amounts of catalyst, and the temperatures used. It is possible, with very high catalyst concentrations, or with increased temperatures, to decrease the reaction time.

Likewise, acrylonitrile is preferred to metha crylonitrile because of greater ease of polymerizability, higher softening points, and the greater solvent resistance of the polymers derived from it. Methacrylonitrile may be used in conjunction with acrylonitrile to increase the susceptibility of the copolymer to solvents. Part of the acrylonitrile, of the order of about 5- to may bereplaced by methacrylonitrile.

The copolymers of this invention are not readily adaptable to the ordinary extrusion methods used in the manufacture of thermoplastic resins, such as, for example, the preparation of cellulose acetate fibers.

The copolymers of this invention containing between 70 and 85% acrylonitrile possess a very high melting-point in excess of 180 C., though at lower temperatures, say about 150 C., they are rather rubbery but still are not sumciently cohesive to be extruded to uniform fibers, films, and sheets free of bubbles, etc. Furthermore, the

pressures required to extrude fine filaments are excessively high.

Copolymers containing more than 55 and less than 70% acrylonitrile have lower softening points and are adapted to extrusion methods. However, when even these copolymers are extruded in this manner, the high temperatures required may cause some reduction in their tensile strength.

Another object of this invention is to provide a method of preparing the fibers, filaments, etc., by shaping a gel of the copolymers of this invention, such as by extruding through suitable orifices, etc. This is accomplished by the use of suitable solvents. The high insolubility of the acrylonitrile copolymers excludes the use of many solvents.

I have found, however, that the nitrohydrocarbon this invention, I dissolve the copolymer in a nitro- 6 hydrocarbon, for example, nitromethane, nitroethane, to produce a solution containing between 8 and 12% of the polymer in the nitrohydrocarbon, cast the films and remove the solvent by evaporation. After the sheet is formed, it is cold drawn during which process molecular orientation takes place along the major axis, The sheet in itself. as prepared, is not molecularly oriented. It is only after the cold drawing process that it exhibits characteristic X-ray diffraction patterns indicative of crystalline orientation. 'The increase in tensile strength and flexibility after the cold drawing is remarkable. On the' other hand, fibers that are spun from th same dilute hydrocarbon solutions are not completely satisfactory. Because of their insolubiiity and because of the use of large amounts of solvent which must be removed, they must be subjected to a long period of heat to remove substantially all of the solvent.

I have now discovered that it is possible to produce more satisfactory sheets, fibers, filaments, and the like from the copolymers of this invention by shaping a gelled mass of the copolymer, as by extrusion. For example, a, copolymer of 70% of acrylonitrile and 15% of a vinyl ether or an acrylic ester and 15% of a vinyl aryl is soluble in nitromethane to the extent of 14%. If this solution is concentrated such as by heat under atmospheric or reduced pressure, the mixture loses the characteristics of a solution and acquires the properties of a gel; that is, the nitrohydrocarbon reverses phase and becomes dissolved in the copolymer, rather than the copolymer dissolved in the nitrohydrocarbon. The gel nature of .this particular copolymer becomes evident at room v temperature at about 15% copolymer and 85% nitromethane. As this gel is heated, the viscosity decreases considerably so that it exhibits a cohesive flow at temperatures of the order. of 55 to C. 7

However, it is not necessary to prepare these gels by first dissolving the polymer in the nitrohydrocarbon and. concentrating the solution. I

may prepare these gels by adding the desired maintained. The extruded form resets as a gel after leaving the orifice and is dried at a low temperature to remove a quantity of the geiation solvent so that the gel does not reliquefy even when heated to progressively higher temperatures.

When produced in this form, the copolymer can be given any desirable shape; such as. by extrusion or calendering and then (1) the gelation solvent removed by suitable means and the formed article cold drawn or 2) part of the gelation solvent is removed and the polymer cold drawn and the remainder of the solvent removed, or (3) none of the gelation solvent may be removed prior to cold drawing. The later method, however, is not the preferred method since these gels are usually weak in their structural properties. The preferred method comprises eleminating some, or a substantial part, of the gelation solvent prior to cold drawing.

The cold drawing may be accomplished at any suitable temperature from room temperature or slightly below up to temperatures of th order of Example '3 Each of the following ratios of acrylonitrile, anacrylic ester and a vinyl aryl compound in which was dissolved 0.2% of benzoyl peroxide was placed in a glass container and polymerized at 50 C. until the polymerization was complete.

a b c Acrylonitrile e 10 7o Ethyl acrylate 20 20 25 Styrene 20 10 The copolymers of the above compositions are dissolved in' nitromethane to give solutions of approximately 5 to 6% of the copolymer in the nitrohydrocarbon. Films are cast from these solutions and the solventallowed 'to evaporate, first at room temperature and then in an oven at 80 C. The average thickness of the films varies from 0.0015 to 0.003 inch with tensile strengths varying from 5,000 to 10,000 pounds per square inch depending upon the amount of acrylonitrile in the copolymer. The films containing the higher acrylonitrile have higher tensile strengths.

Due to the high amount of acrylonitrile, these films are stiff and rigid and not readily subjected to flexing. When cold drawn 200 or 300% at room temperature, a sheet. material exhibiting orientation along the main axis and possessing increased strength and flexibility is obtained.

The increase in tensile strength of these sheets is outstanding, ranging in order from 10,000 to 25,000 pounds per square inch when cold drawn at room temperature. When drawn at higher temperatures, it is possible to achieve a, cold drawing of the order of 300 to 500% and 'to'obtain tensile strengths'in compositions containing at least 70% acrylonitrile to the order of 15,000 to 40,000 pounds per square inch. The yields of the copolymers prepared above are substantially quantitative.

Example 4 The following ratios of components in each of which is dissolved 1% benzoyl peroxide are] placed in glass containers and polymerized under the influence of sunlight for several hours and then placed in an 80 C. oven to complete the polymerization. The copolymers are all tough resins which are soluble in nitromethane. Films were cast from the nitrometha'ne solution and tested before and after drawing from room temperature. Values ranging from,,5,000 to 10,000 pounds per square inch undrawn and 15,000 to 35,000 pounds in the cold drawn condition are obtained.

. after substantially all 8. Example 5 The following example indicates how the copolymer may be prepared in granular form.

The polyvinyl alcohol is dissolved in water prior to the addition of the remaining ingredients.

The mixture is then heated under agitation at 60 to C. until the polymerization is completed. The granular material is in the form of spheres which are filtered ofi, washed with distilled water, and dried in a vacuum oven at 50 C. The copolymer is soluble in nitromethane from which it is possible to produce sheets and fibers of high tensile strength by cold drawing the composition of the nitromethane has been removed. e

Example 6 temperature. This gel can be concentrated under heat to between 18 and 20% solids and when freed of bubbles and solid impurities, it can be extruded through orifices and dried by evaporation of the nitromethane solvent. Fibers or sheet materials obtained in this way are harsh and stifi due to the high concentration of acrylonitrile. When cold drawn, these materials ac- .quire excellent flexibility and possess a considerable increase in strength and exhibit crystalline orientation along the major axis. Filaments produced by this cold drawing process can be drawn into tight knots without breaking.

Emmple 7 The following example indicates the gel process for the preparation of filaments and fibers of the copolymers of this invention. 100 parts of the copolymer of acrylonitrile (70%) and styrene (10 to 5%) and an acrylic ester or vinyl ether (15 to 20%) are introduced into a steam-heated jacketed dough mixer together with- 325 to 360 parts of nitromethane and processed at to 95 C. to produce a highly viscous plastic mass, the characteristics of which are such that, when allowed to cool to room temperature, a, rigid rubbery gel is obtained. This material cannot be filtered readily at room temperature. The highly viscous plastic mass is passed through candle filters at 75 to 95 C. and under pressure to remove contamination, undissolved particles, etc.

The filtered mass is degassed under a vacuum of 2 to 10 inches or higher at 50 to C. The degassed plastic mass is ready for spinning' and is forced by constant pressure pumps through spinnerets. The complete system, that is, the reservoir, spinning pumps, nozzles, etc., and the spinnerets, are maintained at a temperature suincient to keep the mass in a, plastic viscous condition. The temperature of the spinnerets is approximately 65 to 90 0. As the plastic mass leaves the spinneret, the filament is converted to a rigid gel by passing through an immediate area whose temperature is lower than the spinneret temperature.

Example 8 When the vinyl ethers used in the practice of this invention are substituted for the acrylic esters of the preceding examples, results are obtained similar to those of Example 7. An example of special compositions which may be used to yield excellent results is Parts Acrylonitrile 70 Vinyl butyl ether 20 Styrene 10 'in intermediate stages in the Practice of this invention, it is desirable that such solvents have low boiling points so that they may be removed readily frm the copolymer mass. Among suitable nitro hydrocarbon solvents may be mentioned the nitro-aliphatics, such as nitromethane, nitro-ethane, nitropropane, nitrobutane, the nitro-aromatics and the hitro-cyclo aliphatics. Also, there may be used in connection with them, but preferably in minor proportions, certain ketones, for instance, acetone, methyl ethyl ketone, methyl propyl ketone, methyl amyl ketone, acetophenone, phorone, methyl chlorphenyl ketone, methyl nitrophenyl ketone, chlor-ethyl nitrophenyl ketone, diacetone alcohol, acetonyl acetone, acetyl acetone, biacetyl, methyl acetoacetic ester, ethyl acetoacetic ester, etc.; the nitro-alcohols such as, 2-nitro-1-ethanol, 2 nitro-l-propanol, 2-nitro-l-butano1, 2 nitro-l-pentanol, etc.; esters of the aforementioned nitro-alcohols, such as, the formate, the acetate, the propionate, the butyrate, etc.; the ethers of the aforementioned nitro-alcohols, for example, the methyl, the ethyl, the propyl, and the butyl ethers, etc; the cyanoalcohols, for example, lactonitrile, the addition products of the lower-boiling aldehydes and ketones with hydrogen cyanide, for example, the reaction products of hydrogen cyanide with acetaldehyde, propionaldehyde, acetone, methyl ethyl ketone, etc.; the esters of the cyano-alcohols, for example, the formate, the acetate, the propionate, etc.; the ethers of the cyano-alcohols, forexample, the methyl, ethyl, propyl, etc. ethers. Certain phosphates such as trimethyl and triethyl phosphates may likewise be used. The foregoing gelation agents are mentioned by way of illustrasince I believe myself to be the first to discover the possibility of making a gel from the materialsin question and the process of utilizing the gel.

Since it is' extremely diflicult to incorporate plasticizers into the copolymers of this invention by the ordinary milling process, I prefer to accomplish this by adding the plasticizer either to a solution or to a gel of the copolymer in the solvents mentioned heretofore.

By this method, many plasticizers which normally do not possess good compatibility with the polymer may be incorporated into the polymer. Suitable high-boiling plasticizers may be mentioned, the polybasic acid esters of cyano alcohol and of the nitro alcohols, such as, the esters of phthalic, succinic, sebacic, tetrahydrophthalia,

endomethylene tetrahydrophthalic, acetyl citric acids, etc. It is not necessary that all the carboxyl 1o groups of the polybasic acidv be esterifled with the cyano alcohol or the nitro alcohol. Thus, in a. dicarboxylic acid, one carboxyl group may be esterified with the cyanoalcohol and the other with the methyl, ethyl, propyl, butyl alcohols,

etc.; and in a tricarboxylic acid, it is suflicient if one or two of the carboxyl roups are esterifled withthe cyano alcohol and the residual carboxyl groups esteriiied with another alcohol. Also, as suitable plasticizers for the products of this invention may be mentioned the condensation products of acrylonitrile with organic compounds containing active hydrogen such as, for example, the condensation product of an acrylonitrile and acetone wherein the hydrogens of the CH3 groups of the acetone may be substituted by from one to six'p-cyanoethyl groupings, Other plasticizers which may be prepared by the condensation of acrylonitrile with organic compounds containing active hydrogen are the condensation products with alcohols, for example, with phenyl ethyl alcohol, phenoxyethyl alcohol, methoxy diethylene glycol, ethoxy diethylene glycol, phenoxy diethylene glycol, etc., condensation products of acrylonitrile with such compounds as the acetoacetic esters, malonic esters, acetyl acetone, and certain polycyclic hydrocarbons containing active cule, and induce higher compatibilities with the normal ester plasticizers used in the plastics art. As examples of such ester-plasticizers may be mentioned the phosphate esters, such as the triphenyl, tricresyl, xylyl, benzyl, chlorphenyl, nitrophenyl, etc., phosphates; the mixed phosphate esters, such as phenyl dicresyl, diphenyl monocresyl, etc. Other esters, such as dimethyl phthalate, diethyl phthalate, dibenzyl sebacate, dibutyl sebacate, diethylene glycol dihexoate, dibutoxyethyl sebacate, dicrot'yl azeleate, methyl octyl phthalate, octyl chlorbenzoate, tetrahydrofurfuryl sebacate, tetrahydrofurfuryl fumarate, etc.

Preferably those esters are used that have'at least one ester group corresponding to one of the ester groups in the acrylic acid ester or a hydr0 carbon group corresponding to a, hydrocarbon group of the vinyl ether or vinyl aryl compound used in the preparation of the copolymer.

The fibers and smaller articles produced according to this invention may be woven into highly insoluble and chemical resistant cloth for use in filter cloths and handling chemicals and the like. They may also be used for textiles, for example, cloth, hosiery, articles of clothing, etc. In the form of sheets, they may be used as protec tive coatings, awnings; raincoats, shower curtains, aprons, hospital bed sheeting, containers for hydrocarbon oils, gasoline, kerosene, vasoline, ointments, etc.

What I claim as. my invention and desire to secure by Letters Patent of the United States is:

1. A cohesive workable reversible gel adapted to the preparation of shaped or molecularly oriented structures which is essentially (A) a liquid nitrohydrocarbon and (B) the polymerization product of a mixture comprising (1) at least the group consisting of hydrogen and methyl radicals and R is an alkyl radical, and Z is an aryl radical.

2. A cohesive workable reversible gel adapted to the preparation oi." shaped or molecularly oriented structures which is essentially (A) nitromethane and (B) the polymerization product of a mixture comprising- (1) at least 55% but not more than 85% of acrylonitrile, (2) at least 5% but not more than 30% of a compound of the formula CH2=CRZ, and- (3) at least 5% but not more than- 30% of a vinyl ether of the formula CH2=CHOR where R is selected from the group consisting of hydrogen and methyl radicals and R is an alkyl radical, and Z is an aryl radical.

3. A cohesive workable reversible gel adapted to the preparation of shaped or molecuiarly oriented structures which is essentially (A) a nitrohydrocarbon solvent and (B) the polymerization product of a mixture comprising (1) at least 55% but not more than 85% acrylonitrile, (2) at least 5% but not more than 30% of styrene, and (3) at least 5% but not more than 30% of vinyl butyl ether.

12 4. A cohesive workable reversible gel adapted to the preparation oi shaped or moleculariy oriented structures which is essentially (a) a nltroalkyl hydrocarbon solvent containing 1-4 carbon.-

atoms in the alkyl group and (b) the polymerization product of a mixture comprising (1) at least but not more than acrylonitrile (2) at least 5% but not more than 30% of styrene and (3) at least 5% but not more than 30% of vinyl butyl ether.

GAETANO F. DALELIO.

REFERENCES CITED The following references are ofrecor d in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,123,599 Fikentscher et a1. July 12, 1938 2,238,730 Hauile Apr. 15, 1941 1,929,453 Semon Oct. 10, 1933 2,367,493 Fordyce et a1. Jan. 16, 1945 2,359,103 Gerhart et a1. Sept. 26, 1944 2,360,876 Garvey Oct. 24, 1944 FOREIGN PATENTS Number Country Date 519,788 British Apr. 5, 1940 387,976

British Feb. 16, 1933 

